Method for preparing a latex with photochromic properties and uses thereof, particularly in ophthalmology

ABSTRACT

This invention relates to a method for preparing a photochromic latex, photochromic thin films obtained therefrom, and articles coated with such thin films, in particular photochromic ophthalmic lenses.

The object of the present invention is a method for preparing aphotochromic latex, photochromic thin films obtained from the latter,and articles coated with such thin films, in particular photochromicophthalmic lenses.

The phenomenon of photochromic has been known for many years. A compoundis described as photochromic when, for example, this compound,irradiated with a light beam containing some wavelengths in theultraviolet region, changes colour and returns to its original colourwhen the irradiation ceases.

There are many applications of this phenomenon, but one of the mostuseful known applications is in the ophthalmic optics field, in themanufacture of lenses or spectacle glasses, so as to filter the lightradiation as a function of its intensity.

The incorporation of photochromic compounds into an organic materialconstituting an ophthalmic lens gives a glass whose weight isconsiderably less than that of conventional lenses composed of inorganicglass containing silver halides as photochromic agents.

A widely used method for manufacturing ophthalmic lenses fromphotochromic organic material is the method known as “thermal transfer”,in which the organic photochromic compounds, such as spirooxazines orchromenes, are applied to the lens by means of a temporary support suchas a varnish, then the coated lens is heated so as to cause the transferof the photochromic compound of the varnish onto the main surface of thelens. This method is especially disclosed in U.S. Pat. No. 4,286,957 and4,880,667.

Another technique known as “cast-in-place” consists of incorporating thephotochromic organic compounds into a polymerizable mixture leading to atransparent organic material, introducing this into a mould and theninitiating its polymerization.

After removal from the mould, a photochromic ophthalmic lens is obtainedwhose photochromic pigments are incorporated into the bulk of this lens.

This latter technique has two major disadvantages:

It requires considerable quantities of photochromic pigments, which arecompounds whose synthesis is costly.

The initiators used for the polymerization degrade the photochromicpigments, which tends to cause a reduction in their photochromicperformance. In addition, the presence of the degradation products,which are generally coloured, could change the appearance of the finallens, rendering it unsuitable for its use.

In addition, in the two above techniques, since the performances of thephotochromic pigments are closely dependent on the material in whichthey are incorporated, it has been necessary to develop specific organicmaterials suitable for the incorporation of such pigments.

However, some organic materials used in ophthalmic optics such aspolycarbonates (thermoplastic materials generally transformed byinjection moulding) have a polymer matrix which is unsuitable forphotochromic.

An advantageous technique which is an alternative to the thermaltransfer and cast-in-place techniques comprises the application of aphotochromic coating onto a preformed ophthalmic lens.

The nature of the material constituting the ophthalmic lens on which thephotochromic coating is applied is thus no longer relevant.

Such a technique is disclosed in principle, for example in theEP-A-146136 and more particularly, in the case of photochromicpolyurethane varnishes, in the patent application WO 98/37115.

It is thus desirable to develop new photochromic varnishes usable in theophthalmic optics field which show improved properties, in particulargiven the international directives, aimed at the reduction of the use oforganic solvents.

The object of the invention is a method for preparing a latex withphotochromic properties, whose properties change little or not at allover time, leading after drying to thin transparent photochromic films,usable on ophthalmic lenses.

Aqueous emulsions containing a photochromic pigment have already beendescribed in the prior art.

The Russian patent RU-2095836 discloses a method for obtainingphotochromic microcapsules, whose main application is asauthentification agents in official documents.

According to the method disclosed in this patent, a photochromiccompound, in this case 6-nitro-1,3,3-trimethylstyrene(2H-1-benzopyran)-2,2-indoline, is dissolved in a mixture ofmethacrylates of polyfunctional oligoesters (in this case a mixture ofethylene glycol di(meth)acrylate (DMEG) and triethylene glycoldi(meth)acrylate), in the presence of a benzoyl peroxide initiator.

The mixture is emulsified in an aqueous solution containing an ammoniumsalt of a butyl acrylate-methacrylic acid copolymer.

A mixture of a melamine-formaldehyde-polyvinyl alcohol resin isintroduced into the resulting emulsion, then a crosslinked envelope isformed, while simultaneously polymerising the core of the microcapsules.

Moreover, the microcapsules thus formed have a diameter of 3 to 5 μm,which makes them unsuitable for depositing thin layers of 3 to 20 μm.

The microcapsule suspension obtained also has a residual pink colour, inthe absence of irradiation, in the non-excited state, which is notdesirable for ophthalmic use.

The method of preparing a latex with photochromic properties accordingto the invention comprises the following steps:

(1) preparing an aqueous emulsion (I) of a composition A comprising

-   -   at least one organic monomer Z with a C═C group, capable of        free-radical polymerization, and    -   one or more organic photochromic compounds containing a nucleus        of formula:

(2) polymerising composition A of organic monomers in the presence of awater-soluble initiator to obtain said latex with photochromicproperties.

The inventors have observed that by polymerising the monomer or monomersZ and the photochromic compound as defined above in aqueous emulsion, inother words with a water-soluble initiator, a photochromic latex isunexpectedly obtained with the desired properties.

As is well known, latexes are stable dispersions of one or more polymersin an aqueous medium.

Without wishing to give a limitative interpretation to the invention, itis possible that the presence of the initiator in aqueous solutionreduces the contact between the radicals generated in the aqueous phaseand the photochromic compound present in the organic phase, and that thepossible degradation of the photochromic compound is thus minimized.

The recommended polymerizable monomers Z with C═C groups are monomers oftype alkyl (meth)acrylate, preferably of type mono(meth)acrylate.

The preferred monomers Z are selected from the C₁-C₁₀ alkyl(meth)acrylates and preferably mixtures of C₂-C₁₀ alkyl acrylate andC₁-C₃ alkyl methacrylate monomers.

In addition, it has been observed that the performances of thephotochromic pigments are considerably improved when they areincorporated into matrices with a low glass transition temperature.

Thus, it is in general desirable that the final polymer resulting fromthe drying of the latex obtained according to the method of theinvention has a glass transition temperature Tg lower than or equal to0° C.

Thus, at least one monomer Z is preferably capable of forming byhomopolymerization a homopolymer with a Tg lower than 0° C., andpreferably lower than −20° C., and even more preferably lower than −30°C. These monomers are subsequently referred to as “low Tg monomers”.

Low Tg monomers which are particularly recommended include butylacrylate (Tg homopolymer: −55° C.), propyl acrylate and ethyl acrylate.

It is generally desirable to use a mixture of monomers Z composed of alow Tg monomer defined above and at least a second monomer Z able tolead by homopolymerization to a homopolymer with a higher Tg, whichimproves the mechanical properties. These monomers are subsequentlyreferred to as “high Tg monomers”.

High Tg monomers include methyl methacrylate (Tg homopolymer: 105° C.).

The low Tg monomer preferably represents at least 40%, and preferably atleast 50% by weight of the total weight of monomers Z in the compositionA.

A preferred composition A contains a mixture of propyl, butyl or hexylacrylate and methyl, ethyl or propyl methacrylate.

The composition A may also contain one or more crosslinking agents, suchas for example the poly(alkylene glycol) di(meth)acrylates. Preferredcrosslinking agents include glycidyl methacrylate (GMA), which causesboth intraparticular and interparticular crosslinking (in the presenceof piperazine), and di(ethylene glycol) dimethacrylate.

These crosslinking agents may represent up to 10%, but generallyrepresent up to 5% by weight of composition A.

The emulsion copolymerisation of composition A leads, depending on thecase, to homopolymer particles or to random copolymer particles.

The invention also comprises in its scope the case of latexes with atleast biphasic particles, in particular with a structure of thecore/skin type.

Such a structure is obtained by adding to the latex produced from the atleast partial polymerization of composition A a second aqueous emulsion(II) containing a composition B of at least one organic monomer capableof free-radical polymerization, then by polymerising said composition B.

The monomers of composition B are preferably selected from the samefamilies of monomers as those used in composition A.

In this case the monomers Z used in composition B may lead to ahomopolymer with glass transition temperature higher than 0° C., sincethe photochromic pigments are located in the core of the particles.

The more rigid skin leads to better mechanical properties of the filmsfinally obtained.

The organic photochromic compounds which may be used within the scope ofthe invention are photochromic compounds containing a nucleus offormula:

These photochromic compounds preferably do not contain an indoline ring.

The photochromic compounds are preferably naphthopyrans, in particularthose disclosed in documents U.S. Pat No. 5,066,818, WO 93/17071,F-A-2688782.

The preferred naphthopyrans include naphthopyrans with two substitutedor unsubstituted phenyl groups on the carbon adjacent to the oxygen ofthe pyran ring.

It has been observed that such photochromic compounds show excellentresistance to degradation by radicals in aqueous medium.

The photochromic compound is introduced in a quantity sufficient toobtain the desired photochromic effect in the final films.

The concentrations in photochromic compound generally vary from 2 to 5%by weight with respect to the weight of polymerizable monomers presentin the latex.

The water-soluble initiators used for the polymerization of thecompositions of the invention are salts and compounds with at least onehydrophilic function.

These salts and compounds include alkali metal and ammonium persulfates,in particular sodium or potassium persulfate, hydrogen peroxide, and2,2′-azobis(2-amidinopropane) dihydrochloride.

Partially water-soluble peroxides such as succinic peracid and t-butylhydroperoxide may also be used.

Redox systems such as the persulfates combined with a ferrous ion mayalso be used.

Other initiators are cumyl hydroperoxide or hydrogen peroxide in thepresence of ferrous, sulfite or bisulfite ions.

Among these initiators, the preferred initiators are the alkali metalpersulfates.

Sodium or potassium persulfate is preferably used, rather than theammonium salt, which may cause pH variations which can generate coloureddegradation products of the photochromic compound.

The quantity of initiator is variable and may be adapted according tothe case.

In general, the quantity of initiator varies from 0.1 to 1% by weightwith respect to the total weight of polymerizable monomers present inthe latex.

The latex is prepared by mixing the photochromic compound with themonomer(s) Z, generally in aqueous medium, preferably in the presence ofsurface-active agents, then causing the polymerization by means of aninitiator which is preferably added into the above mixtureprogressively, while agitating vigorously.

The surface-active agents may be ionic surface-active agents such assodium dodecyl sulphate, dodecylbenzene sulphate, sodium sulfonate orthe sulphates of ethoxylated fatty alcohols, nonionic such as theamphoteric or ethoxylated fatty alcohols. The preferred system is acombination of ionic and nonionic surface-active agents.

The aqueous emulsion of the composition may also contain a conventionalbuffering agent, which keeps the pH of the emulsion constant (preferablyfrom 5 to 7) during the preparation of the latex.

The polymerization time generally varies from 30 minutes to severalhours.

The initiator and the aqueous emulsion are preferably each introducedprogressively into the reaction medium throughout the polymerizationstep.

During the polymerization, the temperature of the reaction mixture isgenerally between 50 and 90° C., this temperature being necessary toactivate the initiator.

The mixture and the initiator are further preferably introducedconcomitantly into an aqueous solution containing surface-active agents,this solution being termed “starting solution”.

The latexes obtained by the method of the invention have a particlediameter of between 50 and 400 nm, preferably between 80 and 300 nm andeven better between 150 and 250 nm.

The dry extract of the latexes generally represents from 30 to 50% byweight of the total weight of the latex and preferably from 40 to 50% byweight.

A dilution is possible, by addition of water, if it is wished to reducethe dry extract so as to obtain a thinner varnish.

The pH of the latexes according to the invention generally varies from 5to 7.

The photochromic latexes according to the invention may be applied ontoany type of substrate by conventional techniques known to a personskilled in the art, particularly:

by immersion in the bath of photochromic latex (dip coating)

or by application onto the surface of the substrate followed bycentrifugation to ensure a uniform application of the latex onto thesurface.

The latex film is then dried under the following conditions:

Film drying temperature: ambient to 100° C.

Drying time: 5 minutes to 1 hour.

The thicknesses of the films obtained are fixed as a function of theextent of the photochromic effect desired.

Generally, and given the quantity of the photochromic compound presentin the latex, the thickness varies from 3 to 20 μm and preferably from 5to 15 μm.

The preferred substrates onto which the latexes obtained by the methodof the invention are applied are any organic glass substrate currentlyused for organic ophthalmic lenses.

Polycarbonate (thermoplastic) substrates, in particular the ophthalmiclenses manufactured by the Gentex Optics company, are the substratesparticularly recommended onto which the latexes obtained by the methodof the invention are applied.

Among other suitable substrates are the substrates obtained by thepolymerization of alkyl methacrylates, in particular C₁-C₄ alkylmethacrylates such as methyl (meth)acrylate and ethyl (meth)acrylate,allyl derivatives such as the allyl carbonates of linear or branchedaliphatic or aromatic polyols, thio(meth)acrylics, thiourethanes,polyethoxylated aromatic (meth)acrylates such as the polyethoxylatedbisphenolate dimethacrylates.

Recommended substrates include substrates obtained by polymerization ofthe allyl carbonates of polyols such as ethylene glycol bis(allylcarbonate), diethylene glycol bis(2-methyl carbonate), diethylene glycolbis(allyl carbonate), ethylene glycol bis(2-chloroallyl carbonate),triethylene glycol bis(allyl carbonate), 1,3-propanediol bis(allylcarbonate), propylene glycol bis(2-ethylallyl carbonate), 1,3-butenediolbis(allyl carbonate), 1,4-butenediol bis(2-bromoallyl carbonate),dipropylene glycol bis(allyl carbonate), trimethylene glycolbis(2-ethylallyl carbonate), pentamethylene glycol bis(allyl carbonate),isopropylene bisphenol A bis(allyl carbonate).

The substrates particularly recommended are substrates obtained bypolymerization of ethylene glycol bis(allyl carbonate), sold under thetrade name CR 39® by the company PPG INDUSTRIES (lens ORMA® ESSILOR).

Among other recommended substrates are substrates obtained bypolymerization of thio(meth)acrylic monomers, such as those disclosed inthe French patent application FR-A-2 734 827.

The substrates may obviously be obtained by polymerising mixtures of theabove monomers.

It is possible to apply other coatings onto the photochromic film suchas anti-abrasion coatings and anti-reflection coatings.

The hard anti-abrasion coatings may be any anti-abrasion coatings knownin the ophthalmic optics field.

Among the hard anti-abrasion coatings recommended in the presentinvention are coatings obtained from compositions based on silanehydrolysate, in particular the hydrolysate of epoxysilane, as describedin the French patent application No 93 026 49 and the U.S. Pat. No.4,211,823.

As stated above, the ophthalmic lens according to the invention mayadditionally contain an anti-reflection coating deposited on theanti-abrasion coating.

As an example, the anti-reflection coating may be composed of a mono-ormultilayer film, of dielectric materials such as SiO, SiO₂, Si₃N₄, TiO₂,ZrO₂, Al₂O₃, MgF₂ or Ta₂O₅, or their mixtures.

It is thus possible to prevent the appearance of a reflection at thelens-air interface.

This anti-reflection coating is generally applied by vacuum depositaccording to one of the following techniques:

-   -   by evaporation, optionally assisted by ion beam;    -   by ion-beam spraying;    -   by cathodic spraying;    -   by chemical vapour deposit assisted by plasma.

In addition to vacuum deposit, it is also possible to deposit aninorganic layer by the sol/gel route (for example from tetraethoxysilanehydrolysate).

In the case of a single layer film, its optical thickness must be equalto λ/4,(λ is a wavelength between 450 and 650 nm).

In the case of a multilayer film comprising three layers, a combinationmay be used corresponding to the respective optical thicknesses λ/4,λ/2, λ/4 or λ/4, λ/4, λ/4.

It is also possible to use an equivalent film formed by more layers, inthe place of any number of the layers which are part of the above threelayers.

The present invention also relates to latexes with photochromicproperties comprising polymer particles as defined above which containan effective quantity of at least one photochromic compound as definedabove.

The following examples illustrate the present invention.

In the examples, except where otherwise stated, all the percentages andparts are expressed by weight.

Preparation of a Random Butyl Acrylate (ABu)-methyl Methacrylate (MMA)Latex with Photochromic Properties.

Preparation of the Starting Solution

0.82 g of surface-active agent DISPONIL® A 3065 (mixture of fattyalcohols of 30 EO, 65% active matter) and 0.55 g of surface-active agentDISPONIL® FES (C₁₂₋₁₄(OCH₂CH₂)₁₂ OSO₃-Na⁺) were dissolved in 148.9 g ofwater. The mixture was agitated for 10 minutes, then introduced into adouble-wall reactor whose cap had five inlets (for the nitrogen, thethermometer, the stirrer, the initiator inlet and the emulsion inlet).

The mixtures is degassed for 1 hour at 70° C.

Preparation of the Emulsion I

At the same time, 7.36 g of DISPONIL® A 3065 and 4.8 g of DISPONIL® FESwere dissolved in 164.8 g of water buffered by the addition of 0.57 g ofNaHCO₃. The solution was agitated, then, still under agitation, amixture was added of 185.7 g of butyl acrylate and 79.6 g of methylmethacrylate into which had previously been incorporated 11.7 ofphotochromic compound Pch:8-methoxy-3-(2-fluorophenyl)-3-(4-methoxyphenyl)-3H-naphtho[2,1-b]pyran,whose synthesis is described in the document WO 93/17071. The quantityintroduced corresponded to 4.41% by weight of compound Pch with respectto the weight of the monomers ABu and MMA.

Preparation of the Initiator Solution

In parallel, 1.6 g of sodium persulfate were dissolved in 12.4 g ofwater.

Preparation of the Photochromic Latex

The emulsion I and the initiator solution were added to the reactor, bythe appropriate inlets, over 4 hours and in parallel. (The addition ofthe first drop of sodium persulfate was taken as time zero of thepolymerization reaction). The reaction temperature was 70° C.

The product obtained was a photochromic random 70/30 butylacrylate/methyl methacrylate latex according to the invention with thefollowing properties: Dry extract (%) Particle size (nm) pH 42 180 7

Preparation of a Second Photochromic Random ABu(60)-MMA(40) Latex

The latex was prepared under the same conditions as above except thatthe quantities of monomers used were:

-   -   ABu 161.9 g    -   107.4 g

The quantity of photochromic compound Pch added was 4.34% with respectto the weight of the ABu and MMA monomers.

The product obtained was a photochromic random 60/40 butylacrylate/methyl methacrylate latex with the following properties: Dryextract (%) Particle size (nm) pH 43 190 7

Preparation of a 70/30 ABu-MMA Latex with a Core/Skin Structure

The core of the latex was prepared by adding the emulsion I over 2 h 48min in a first stage, then the skin by adding emulsion 11 over 1 h 12min in a second stage.

The initiator solution was added in parallel to the reaction mixture,over 4 hours as from the addition of the first drop of emulsion I.

The compositions of the starting solution, emulsions I and II and theinitiator solution are given in the following table: Starting solutionemulsion I emulsion II Initiator Water (g) 148.9 115.4 49.4 12.4DISP.3065 0.82 5.15 2.21 (g) (2% w/w) DISP.FES (g)(2%) 0.55 3.36 1.44NaHCO3 (g) 0.4 0.17 ABu (g) 185.7 MMA (g) 79.6 Sodium 1.6 persulfate (g)Pch (4.41% w/w) 11.7

The product obtained was a photochromic core/skin 70/30 butylacrylate/methyl methacrylate latex according to the invention with thefollowing properties: Dry extract (%) Particle size (nm) pH 44 210 7

The performances of the photochromic compounds deposited as film areshown on FIGS. 1 and 2 (Spectral transmission as a function of time).

(Random ABu(70)/MMA(30) latex (FIG. 1), and core/skin latex describedabove (FIG. 2)).

The latex films were deposited on plain ORMA® lenses by centrifugationat thickness 6 μm.

The spectro-kinetic properties of the films were measured under thefollowing conditions:

-   -   Temperature: 20° C. (air regulation)    -   No visible lighting    -   UV lighting: 10.2 W/m²    -   minutes coloration by UV irradiation as defined above/30 minutes        decolouration after stopping UV irradiation.

1-23. (canceled)
 24. A method for preparing a latex with photochromicproperties comprising: preparing an aqueous emulsion (I) of acomposition A comprising: at least one organic monomer Z, wherein saidat least one monomer is further defined as comprising a C═C group andbeing capable of free-radical polymerization, and one or more organicphotochromic compounds containing a nucleus of formula:

 and polymerizing composition A in the presence of a water-solubleinitiator to obtain particles of an at least partially polymerized latexwith photochromic properties.
 25. The method of claim 24, wherein thewater-soluble initiator (i) is introduced progressively to the aqueousemulsion (I), during the polymerization, or (ii) and the aqueousemulsion (I) are each introduced progressively into a reaction mediumthroughout polymerization, or (iii) is an alkali or ammonium persulfate.26. The method of claim 25, wherein the water-soluble initiator isintroduced progressively to the aqueous emulsion I, during thepolymerization.
 27. The method of claim 25, wherein the water-solubleinitiator and the aqueous emulsion (I) are each introduced progressivelyinto a reaction medium throughout polymerization.
 28. The method ofclaim 25, wherein the water-soluble initiator is an alkali or ammoniumpersulfate.
 29. The method of claim 25, wherein the water-solubleinitiator is potassium or sodium persulfate.
 30. The method of claim 24,wherein the least one monomer Z is a low Tg monomer which leads to ahomopolymer the glass transition temperature of which is less than orequal to 0° C.
 31. The method of claim 30, wherein the low Tg monomerrepresents at least 40% by weight of the monomers capable offree-radical polymerization.
 32. The method of claim 24, wherein asubstrate comprises a film of the latex and wherein the substratecomprises an anti-abrasion coating on the latex film, or ananti-reflection coating on the latex film, or an anti-abrasion coatingon the latex film and an anti-reflection coating on the anti-abrasioncoating.
 33. The method of claim 32, wherein the substrate comprises ananti-abrasion coating.
 34. The method of claim 32, wherein the substratecomprises an anti-reflection coating.
 35. The method of claim 32,wherein the substrate comprises an anti-abrasion coating on the latexfilm and an anti-reflection coating on the anti-abrasion coating. 36.The method of claim 32, wherein the substrate is an ophthalmic lens. 37.The method of claim 24, wherein composition A comprises only one type oforganic monomer Z.
 38. The method of claim 24, wherein composition Acomprises more than one type of organic polymer Z.
 39. The method ofclaim 24, wherein the latex is a fully polymerized latex.
 40. The methodof claim 24, wherein the latex is a partially polymerized latex.
 41. Themethod of claim 24, wherein the percentage by weight of the initiatorwith respect to total organic weight of monomer or monomers capable offree-radical polymerization used for the preparation of the latex isbetween 0.1 and 1%.
 42. The method of claim 24, wherein the organicmonomer Z is an alkyl (meth)acrylate monomer.
 43. The method of claim24, wherein the particles of the latex are further defined as having adiameter of 50 to 400 nm.
 44. The method of claim 24, wherein a dryextract of the latex represents from 30 to 50% of the total weight ofthe latex.
 45. The method of claim 24, wherein the pH of the latex isbetween 5 and
 7. 46. A latex with photochromic properties, furtherdefined as comprising particles of a polymer material resulting from thefree-radical polymerization of at least one monomer Z with a C═C groupcomprising one or more organic photochromic compound comprising anucleus of formula:

the particles of said polymer material having an average size of between50 and 400 nm.
 47. The latex of claim 46, wherein the particles arefurther defined as having an average size of between 80 and 300 nm. 48.The latex of claim 47, wherein the particles are further defined ashaving an average size between 150 and 250 nm.
 49. The latex of claim46, wherein the organic photochromic compound is further defined as notcontaining an indoline ring.
 50. The latex of claim 46, wherein a dryextract of the latex represents from 30 to 50% of the total weight ofthe latex.
 51. A substrate comprising a dry latex film with photochromicproperties, the latex further defined as comprising particles of apolymer material resulting from the free-radical polymerization of atleast one monomer Z with a C═C group comprising one or more organicphotochromic compound comprising a nucleus of formula:

the particles of said polymer material having an average size of between50 and 400 nm.
 52. The substrate of claim 51, wherein the film has athickness of between 3 and 20 μm.
 53. The substrate of claim 51, furtherdefined as comprising an anti-abrasion coating.
 54. The substrate ofclaim 51, further defined as comprising an anti-reflection coating. 55.The substrate of claim 51, further defined as comprising ananti-abrasion coating on the latex film and an anti-reflection coatingon the anti-abrasion coating.
 56. The substrate of claim 51, furtherdefined as an ophthalmic lens.
 57. The method of claim 43, wherein theparticles of the latex are further defined as having an average size ofbetween 80 and 300 nm.
 58. The method of claim 57, wherein the particlesare further defined as having an average size between 150 and 250 nm.59. The method of claim 24, wherein the organic photochromic compound isfurther defined as not containing an indoline ring.
 60. The method ofclaim 24, wherein the latex is further defined as a dry latex film. 61.The method of claim 60, wherein the dry latex film has a thickness ofbetween 3 and 20 μm.
 62. The method of claim 24, wherein a substratecomprises the latex.
 63. The method of claim 62, wherein the substrateis further defined as an ophthalmic lens.